#include <stdio.h>

int main()
{
	long double sum=0;//
	int i;
	long double count=1;//
	for(i=1;i<=30;i++)
	{
		count*=i;
		sum+=count;
	}
	printf("%.2Le",sum);//
	return 0;
}
//1+1*2+1*2*3+1*2*3*4+......
//科学计数法%e或者%E